1. Field of the Invention
This invention relates to transformers and more particularly to voltage regulating transformer.
2. Description of the Prior Art
The principle of varying the voltage of a transformer by controlling its leakage flux is broadly old in the art. For example, in U.S. Pat. No. 2,245,192 the output voltage of a transformer is varied by varying the reluctance of both the main flux and leakage flux paths of the transformer. To effectuate this control, parallel flux paths are fabricated in the main core of the transformer. Basically, the transformer has a non-conventional structure. Primary and secondary windings are seated on the main core, while saturating windings are seated on the parallel flux paths of the main core. An auxiliary core carrying saturating windings is positioned in shunt relationship and is encompassed by the main core. The patent does not disclose how the auxiliary core is supported relative to the main core. However, one would imagine that a support means of some kind is necessary to support the auxiliary core since this core is not in contact with the main core. Also the setting of the air gap and/or air gaps between the main core and the auxillary core is not disclosed. However, due to the high reluctance characteristics of air to the flow of magnetic flux, unless the air gap and/or air gaps are within a certain specification, the effect of the auxiliary core on the main core is negligible. In fact, if the setting of the air gap and/or gaps is too wide, then the structure will no longer function as a voltage regulator since the leakage flux which is necessary to achieve voltage regulation will confine itself to flow in the main core rather than shunting to the auxiliary core.
In an attempt to ward off the non-regulating dilemma, the main core is fabricated with parallel flux paths. However, the incorporation of parallel flux paths tends to increase the complexity of the transformer. Due to the complexity of the magnetic structure and the need for the critical setting of the air gap and/or air gaps, the overall cost of the transformer tends to increase.
Another obvious limitation is that the transformer does not readily fit into a compact machine where space is limited.
Various attempts have been made in the prior art to design sturdy, rugged and compact voltage regulating transformers. In U.S. Pat. No. 1,614,254, a regulating transformer which regulates the voltage across a telephone receiver is disclosed. The transformer consists of a centrally located plate made of a permalloy material with two core sections arranged in space relationship but abutting said plate. Control windings are seated on each core section. The magnetic characteristic of the plate is such that, when the voltage across the receiver is within its predetermined range, the reluctance of the plate is minimal. By positioning the winding on the cores to be in series, the reluctance of the transformer is such that shunt loss is minimal. Whenever the voltage across the telephone lines rises the flux through the transformer increases. This increases the permeability of the plate until a maximum value is reached. With the permeability of the core less than maximum the flux is forced to follow the individual cores. However since the coils are connected in series in opposing relationship the flux produced by the current in one winding tends to neutralize the flux produced by the current in the other winding. The net result is that more current flows from the telephone line into the transformer. This in turn increases the reluctance of the plate. This process continues until a point is reached above which the voltage across the terminals of the telephone receiver cannot be increased.
The limitation on the above device is that the degree of voltage regulation is limited (i.e. narrow). This limitation stems from the fact that the voltage regulation is dependent on a fixed variable (i.e. the magnetic characteristics of the treated plate.) The device is not suitable for use in an environment where the voltage regulating range is variable.